Institute of Astronomy

MHD turbulence and state changes in compact X-ray sources

SpeakerTalk DateTalk Series
Steve Balbus (Oxford)6 February 2014Institute of Astronomy Colloquia

Abstract

*Abstract*

There is evidence that the saturation levels of MHD turbulence are
sensitive to the ratio of the small scale viscosity to resistivity,
a quantity known as the magnetic Prandtl number Pm. This sensitivity is present when Pm ~ 1.

Interestingly, discs associated with compact X-ray sources have such a low-to-high (tracking inward) Pm transition radius on scales of tens of Schwarzschild radii. These disc sources are also known for their dramatic changes in their spectral states.

In this talk, I will show that standard alpha disc theory predicts Dwarf-Nova like outbursts when the turbulent stress is even a modestly increasing function of Pm. Implications for understanding the X-ray data will be presented, both successes of the theory and remaining challenges.

Presentation

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